Back to article

Figures and tables

The gravitas of gravitational isotope fractionation revealed in an isolated aquifer

T. Giunta1#,

1Laboratoire de Géochimie des Isotopes Stables, Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Université Paris-Diderot, UMR 7154 CNRS, 1 rue Jussieu, F-75005 Paris, France
#New affiliation: Earth Sciences Department, University of Toronto, 22 Russell Street, M5S3B1 Toronto, Canada

O. Devauchelle2,

2Laboratoire de Dynamique des Fluides, Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Université Paris-Diderot, UMR 7154 CNRS, 1 rue Jussieu, F-75005 Paris, France

M. Ader1,

1Laboratoire de Géochimie des Isotopes Stables, Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Université Paris-Diderot, UMR 7154 CNRS, 1 rue Jussieu, F-75005 Paris, France

R. Locke3,

3Illinois State Geological Survey, 615 E. Peabody Drive, Champaign, Illinois 61820, USA

P. Louvat4,

4Géochimie des Enveloppes Externes, Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Université Paris-Diderot, UMR 7154 CNRS, 1 rue Jussieu, F-75005 Paris, France

M. Bonifacie1,

1Laboratoire de Géochimie des Isotopes Stables, Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Université Paris-Diderot, UMR 7154 CNRS, 1 rue Jussieu, F-75005 Paris, France

F. Métivier2,

2Laboratoire de Dynamique des Fluides, Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Université Paris-Diderot, UMR 7154 CNRS, 1 rue Jussieu, F-75005 Paris, France


P. Agrinier1

1Laboratoire de Géochimie des Isotopes Stables, Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Université Paris-Diderot, UMR 7154 CNRS, 1 rue Jussieu, F-75005 Paris, France

Affiliations  |  Corresponding Author  |  Cite as  |  Funding information

Giunta, T., Devauchelle, O., Ader, M., Locke, R., Louvat, P., Bonifacie, M., Métivier, F., Agrinier, P. (2017) The gravitas of gravitational isotope fractionation revealed in an isolated aquifer. Geochem. Persp. Let. 4, 53-58.

ANR CO2FIX (ANR-08-PCO2-003-03) and the IPGP/Ademe/Schlumberger/Total CO2 geological storage program.

Geochemical Perspectives Letters v4  |  doi: 10.7185/geochemlet.1736
Received 15 May 2017  |  Accepted 3 August 2017  |  Published 26 September 2017
Copyright © 2017 European Association of Geochemistry




Table 1 Porewaters sampled at nine discrete depths within the MSS from a single, multi-level observation well. All data except the δ37Cl and δ81Br were measured at the ISGS (Panno et al., 2013

Panno, S.V., Hackley, K.C., Locke, R.A., Krapac, I.G., Wimmer, B., Iranmanesh, A., Kelly, W.R. (2013) Formation waters from Cambrian-age strata, Illinois Basin, USA: Constraints on their origin and evolution. Geochimica et Cosmochimica Acta 122, 184–197.

; Labotka et al., 2015

Labotka, D.M., Panno, S.V., Locke, R.A., Freiburg, J.T. (2015) Isotopic and geochemical characterization of fossil brines of the Cambrian Mt. Simon Sandstone and Ironton–Galesville Formation from the Illinois Basin, USA. Geochimica et Cosmochimica Acta 165, 342–360.

). δ37Cl and δ81Br were measured at IPGP. Errors are reported in 2σ.
          SampleDepth (m)T (°C)TDS (g/L)[Cl-] mmol/L[Br-] mmol/LCl/Br δ18O–SMOW
(±0.6) ‰
δD–SMOW
(±4.0) ‰
δ37Cl–SMOC
(±0.10) ‰
δ81Br–SMOB
(±0.24) ‰
Upper Mt. Simon

VWS 9-171446150.825046.2404-4.9-32-0.90-0.45

VWS 8-177048172.927326.9396-5-34-0.500.11
Lower Mt. Simon

VWS 7-194450203.833718.6392-3.8-25-0.490.02

VWS 6-201051205.333978.7390-3.6-25-0.270.29

VWS 5-20364820333418.4398-2.9-23-0.210.32

VWS 4-207248205.534148.7392-2.8-22-0.030.86

VWS 3-210550207.333849.3364-2.9-230.180.91

VWS 2-211650208.533629374-3-240.181.17
Back to article | Download in Excel


Figure 1 Isotope ratios and concentrations co-variations in the Upper (black diamonds) and in the Lower units (white diamonds). δ37Cl and δ81Br are apparently linearly correlated (R2 = 0.95) throughout the MSS (a). This linear correlation cannot be attributed to mixing between the Upper and Lower porewaters given the absence of inverse correlation with concentrations (b,c). Instead, this correlation is explained by gravitational settling affecting both systems. Errors are 2σ.
Back to article | Download in Powerpoint


Figure 2 The gravitation-diffusion equilibrium slope dependence on temperature. When z is sufficiently small, Eq. 1 might be simplified to a first order approximation such that                                           where the enrichment of the isotopic ratio is therefore linearly correlated to depth. This approximation attests that for a given isotopic system, the slope of the equilibrium will only depend on the temperature. We report Cl- and Br- concentrations (a,c), as well as δ37Cl and δ81Br (b,d) from the Lower unit aquifer, together with equilibrium enrichment profiles calculated for temperatures of 50 °C (actual temperature of the formation) and of 130 °C (cementation temperature; though highest temperature reached during burial was probably closer to 150 °C). Given the scale of the concentration plots (a,c) 50 °C and 130 °C equilibrium profiles are not distinguishable. Error is 2σ.
Back to article | Download in Powerpoint


Figure 3 Concentrations and isotopic distributions for Cl (a,b) and for Br (c,d) reported with depth in the MSS. EC is the Eau-Claire Shale and PC is the Precambrian basement. We hypothesise the following scenario: 1) An all homogeneous (in concentrations and in isotope compositions) motionless fluid in the MSS (thin black line). 2) The cementation of the Middle unit occurred relatively rapidly, before equilibrium is reached throughout the entire MSS (dashed line). 3) Disconnected Upper and Lower aquifers then separately pursue their evolution toward equilibrium (blue shaded areas). The concentration decrease in the Upper unit (a,c) is then resulting from a dilution event (as proposed by Panno et al., 2013) which must have occurred after stage (2).
Back to article | Download in Powerpoint

Back to article

Supplementary Figures and Tables



Figure S-1 Gravity settling of chlorine in a still aquifer. (a) Evolution of the concentration profile. (b) Relaxation of the amplitude of the concentration profile C(z = 0) C(z = h). Equilibrium corresponds to Eq. S-4, Fourier mode to Eq. S-19, and numerical simulations to Eq. S-11. Parameters estimated for the LMS aquifer (Table S-1).
Back to article | Download in Powerpoint

Table S-1 Quantities used in A.4. Brackets indicate typical range.
NameSymbolTypical value
Boltzmann constant1.38 x 10-23 J K-1
Avogadro constant6.02 x 1023 mol-1
Acceleration of gravity9.81 m s-1
Density of water1000 kg m-3
Solute concentration[2. 10] mol L-1
Elevation[0. 400] m
Water temperature324 K (50 °C)
Tortuosity of the porous matrix10
Partial molar volume (Cl)21.6 cm3 mol-1
Partial molar volume (Br)28.6 cm3 mol-1
Molar mass (Cl)35.5 g mol-1
Molar mass (Br)79.9 g mol-1
Diffusion coefficient in free water (Cl)2.5 x 10-9 m2 s-1
Diffusion coefficient in free water (Br)2.5 x 10-9 m2 s-1
Diffusion coefficient in porous matrix (Cl)2.5 x 10-11 m2 s-1
Diffusion coefficient in porous matrix (Br)2.5 x 10-11 m2 s-1
Settling velocity in free water (Cl)1.06 x 10-13 m s-1
Settling velocity in free water (Br)4.42 x 10-13 m s-1
Settling velocity in porous matrix (Cl)1.06 x 10-15 m s-1
Settling velocity in porous matrix (Br)4.42 x 10-15 m s-1
Back to article | Download in Excel

Table S-2 This Table is similar to the one presented in the main text (Table 1). In addition we added the Cl and Br concentrations and isotopic compositions measured in the Ironton-Galesville Sandstone, the Cambrian formation covering the Eau-Claire Shale. Isotopic data are reported versus Standard Mean Oceanic Chloride and Bromide, respectively. Error is 2σ.
        SampleDepth (m)TDS (g/L)[Cl-] mmol/L[Br-] mmol/LCl/Br δ37Cl– SMOC (±0.10) ‰δ81Br– SMOB (±0.24) ‰
Ironton-Galesville

VWS 11-149963.610172.3442.20.021.43

VWS 10-152468.911102.4462.5-0.08-0.35
Upper Mt. Simon

VWS 9-1714150.825046.2404-0.90-0.45

VWS 8-1770172.927326.9396-0.500.11
Lower Mt. Simon

VWS 7-1944203.833718.6392-0.490.02

VWS 6-2010205.333978.7390-0.270.29

VWS 5-203620333418.4398-0.210.32

VWS 4-2072205.534148.7392-0.030.86

VWS 3-2105207.333849.33640.180.91

VWS 2-2116208.5336293740.181.17
Back to article | Download in Excel


Figure S-2 (a) The Illinois Basin (bright coloured) and the different geological structures surrounding it. Decatur is the location chosen for the CO2 sequestration project and is therefore the location of the multi-level observation borehole where porewaters were sampled. (b) Geological cross section of the Illinois Basin between A and A’. The Mount Simon Formation corresponds to the deepest strata of the Cambrian units. Figures modified after Panno et al. (2013).
Back to article | Download in Powerpoint


Figure S-3 Stratigraphic column from the igneous basement to the Ironton-Galesville Sandstone and the approximate depth for each different unit. Red circles indicate the depth at which porewaters were sampled in the course of the Decatur Project. Figure modified after Labotka et al. (2015).
Back to article | Download in Powerpoint


Figure S-4 White diamonds are referring to samples from the Lower Mount Simon (LMS), black diamonds are referring to the samples from the Upper Mount Simon (UMS) and grey circles are referring to IG. We reported the isotopic compositions versus the inverse of the concentrations. Here we also plotted the data for the Ironton-Galesville formation, in order to show that Ironton-Galesville brines cannot neither be associated to any possible mixing with any of the units from the Mount Simon Sandstone.
Back to article | Download in Powerpoint